Re: [PATCH v5 1/5] iommu: Return -EMEDIUMTYPE for incompatible domain and device/group

[Jason Gunthorpe]

On Fri, Jul 01, 2022 at 02:44:51PM -0700, Nicolin Chen wrote:
> Cases like VFIO wish to attach a device to an existing domain that was
> not allocated specifically from the device. This raises a condition
> where the IOMMU driver can fail the domain attach because the domain and
> device are incompatible with each other.
> 
> This is a soft failure that can be resolved by using a different domain.
> 
> Provide a dedicated errno from the IOMMU driver during attach that the
> reason attached failed is because of domain incompatability. EMEDIUMTYPE
> is chosen because it is never used within the iommu subsystem today and
> evokes a sense that the 'medium' aka the domain is incompatible.
> 
> VFIO can use this to know attach is a soft failure and it should continue
> searching. Otherwise the attach will be a hard failure and VFIO will
> return the code to userspace.
> 
> Update all drivers to return EMEDIUMTYPE in their failure paths that are
> related to domain incompatability. Also remove adjacent error prints for
> these soft failures, to prevent a kernel log spam, since -EMEDIUMTYPE is
> clear enough to indicate an incompatability error.
> 
> Add kdocs describing this behavior.
> 
> Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> Reviewed-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
> ---
>  drivers/iommu/amd/iommu.c                   |  2 +-
>  drivers/iommu/apple-dart.c                  |  4 +--
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 15 +++--------
>  drivers/iommu/arm/arm-smmu/arm-smmu.c       |  5 +---
>  drivers/iommu/arm/arm-smmu/qcom_iommu.c     |  9 ++-----
>  drivers/iommu/intel/iommu.c                 | 10 +++-----
>  drivers/iommu/iommu.c                       | 28 +++++++++++++++++++++
>  drivers/iommu/ipmmu-vmsa.c                  |  4 +--
>  drivers/iommu/omap-iommu.c                  |  3 +--
>  drivers/iommu/s390-iommu.c                  |  2 +-
>  drivers/iommu/sprd-iommu.c                  |  6 ++---
>  drivers/iommu/tegra-gart.c                  |  2 +-
>  drivers/iommu/virtio-iommu.c                |  3 +--
>  13 files changed, 47 insertions(+), 46 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Jason